This invention relates generally to a yarn brake and particularly to a weft yarn braking system for a weaving machine or loom that utilizes a plurality of weft yarns and inserts said yarns selectively into a warp shed.
Multiple weft looms have been known, wherein a multiple weft yarn supply is positioned outside of the warp shed along with a weft yarn braking mechanism. The yarn braking mechanism is usually actuated by means of an operative connection to the loom, so as to release a particular weft yarn at the start of the picking operation. For example, the yarn braking mechanism is connected by a cam which is driven by the main shaft of the loom. In use, the cam releases the yarn brake at a particular point during the cycle of the loom operation and re-applies the yaarn brake at some other period of time during the cycle. The later periods of time have always been predetermined and have always been the same.
In another known loom illustrated in U.S. Pat. No. 3,565,121 issued on Feb. 23, 1971 to Vladimir Svaty for weft selecting and presenting apparatus, several differently colored weft yarns are fed through a single braking means of the loom. In this loom, only the selected weft yarn is clamped by the braking means and tensioned by the tensioning means during insertion into the gripper shuttle and after the pick of the gripper shuttle. The selected weft yarn is untensioned during the weft insertion cycle of the loom. In this loom, the yarns which were not selected remain untensioned and are not clamped. The weft yarns on one end of the loom all pass through or between two braking members, one of which is fixed and the other which is movable against the fixed braking member. The movable braking member is urged by a spring against the fixed member so as to exert a light tension on the yarn, so that the yarn can be taken off of the supply bobbin without causing yarn breakage or uncontrolled unwinding. This braking means, however, includes an electromagnetic coil which is selectively energized to clamp the weft yarn to prevent the yarn from being unwound from the supply bobbin. When it is desired to pick yarn from one particular end, the coil is de-energized so that the yarn may be drawn through the yarn braking device with very little tension being exerted thereon.
This device has two significant disadvantages. The first one is that light tension has to be applied to the yarn at all times by the spring urging the movable member towards the fixed member, even during the yarn insertion phase of the loom. This, in turn, causes undue wear on the parts which must guide the yarn into the warp shed and puts an undue strain on the yarn itself, and thus limits the speed of weft insertion. The second disadvantage is that the yarns not being inserted into the warp shed but passing through the same tension device or weft braking device will only be lightly gripped and will not be clamped. This permits the slack take-up member as seen in FIG. 8 of this patent to exert force on the yarn and, coupled with loom vibration, to draw excess yarn through the tensioning device. This produces excessive slack in the yarn, resulting in false loom stops by the stop motion which detects a broken yarn, even through the yarn has not become broken but has just become excessively slack and hinders attempts to correctly position the weft.
The principal object of this invention is to provide an improved yarn brake for textile machine which can be selectively operated for applying braking pressure to the yarn, so as to apply full tension, partial tension, or no tension to the yarn.
Another object of this invention is to provide a weft yarn braking system for a loom using the improved brake to control the tension on each of the individual yarns precisely, so that when a particular yarn is being fed into the warp shed during insertion of the weft yarn from one side of the loom to the other, all tension is released from the yarn and a partial tension is re-imposed upon the yarn near the end of the weft insertion. During all other times, a full gripping tension is imposed on the yarn.
These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings.